The present invention relates to a mechanical seal system to prevent fluid leakage along a shaft extending through a housing, and more particularly to a sealing system for a shaft in a housing providing a temporary face seal under static conditions and a non-contacting dynamic seal operative upon rotation of the shaft.
Numerous prior seal constructions have been developed attempting to provide an effective sealing means for the prevention of fluid leakage between a rotating shaft and the housing therefor. Such sealing devices fall into the catagories of continuous contact seals, labyrinth-type seals and hydrodynamic seals. Of concern in the present invention is the sealing of low to medium pressure liquid around high speed shafts where the shaft is rotating at a speed of over 5000 revolutions per minute. The opposing requirements of such a system are minimum or no leakage and minimum torque or wear versus maximum life. These requirements can be ideally reconciled by the present seal system.
Among the objects of the present invention is the provision of a mechanical seal system having a non-contracting hydrodynamic seal to initiate and sustain fluid flow in a direction opposite to the direction of leakage along a shaft in a housing during rotation thereof. The hydrodynamic seal is in the form of a helix or screw element which is formed either on the rotating shaft or on the cylindrical wall surrounding the shaft and provides the solution to the requirement of minimum or no leakage, no wear, and long life. These functions, however are provided only under dynamic conditions where the helix performs as a viscous shear pump above the minimum shaft speed necessary for this type of seal. In the absence of these operational conditions, leakage would occur through the helix pump clearance.
Another object of the present invention is the provision of a mechanical seal system utilizing a temporary contact or face seal to prevent leakage along the shaft under generally static conditions when the hydrodynamic seal becomes partially or fully inoperative. This temporary seal includes a stationary face ring mounted in the housing and a rotating face seal flexibly attached to and rotating with the rotatable shaft. The rotary face seal is spring-loaded and hydrostatically balanced so as to be urged toward the stationary face ring and provide sealing contact therewith. The seal is also equipped with an unloading device activated as a result of rotation of the shaft to retract the rotary face seal as the helix-induced flow approaches and then effects fluid sealing.
Further objects are to provide a construction of maximum simplicity, efficiency, economy and ease of assembly and operation, and such further objects, advantages and capabilities as will later more fully appear and are inherently possessed thereby.